During the fabrication of automobiles, trucks, and similar over-the-road vehicles, many body components present structural members having cavities that require sealing to prevent the entrance of moisture and contaminants which can cause corrosion of the body parts. It is generally desirable to strengthen the members while maintaining their light weight. It is also beneficial to stabilize these members in order to attenuate and dampen noise and vibrations that would otherwise be transmitted along the length or passage of the cavity. Many of these cavities are irregular in shape or narrow in size, thus making them difficult to properly seal.
Polyurethanes are a class of materials that can be used to prepare rigid foams and are potentially useful for forming the type of reinforcing, sealing, and/or acoustic damping members described above. Polyurethanes are prepared by combining one or more polyols with one or more polyisocyanates. Commonly used polyisocyanates include aromatic diisocyanates, such as methylene diphenyl diisocyanate (“MDI”) and toluene diisocyanate (“TDI”), as well as oligomers or polymers thereof.
Many known polyisocyanates are supplied with significant levels (more than 20%) of free isocyanate monomer. The reaction temperatures used to drive the polyurethane formation process typically raise the vapor pressure of the unreacted monomer and cause it to volatilize. Due to the toxicity of certain isocyanate monomers, additional steps are often taken to reduce their atmospheric concentration in areas to which personnel are exposed. In some instances, ventilated structures such as “down draft booths” are provided to minimize personnel exposure to the volatilized monomers. However, providing such ventilated structures can be costly and difficult. Thus, a need has arisen for a polyurethane foam that addresses the foregoing issues.